taru-adjective, adverb taking the 'to' particle
glaring; piercing; penetrating
Literary expression describing eyes that are sharp, bright, and intense, often suggesting keen insight or strong emotion. Used as a taru-adjective or adverbially with と.
彼は炯々とした目で相手をにらんだ。
He glared at his opponent with piercing eyes.
老人の目は今も炯々と輝いていた。
The old man's eyes still shone brightly and sharply.
Rarely used kanji form; 烱 is a variant of 炯.
The exact derivation is uncertain; the kanji 炯 and 烱 both carry the meaning 'bright, shining', and the reduplicated form emphasizes intensity. The word is used in classical and literary Japanese to describe a sharp, glaring light, especially of the eyes.